The present invention relates to the field of antennas and wireless communication of electromagnetic radiation. In particular, the present invention relates to a waveguide network for connecting to a flat panel array of antenna elements.
Antennas are generally passive devices which radiate or receive electromagnetic radiation, and an antenna""s receiving properties can be derived from its transmitting characteristic or vice versa. The antenna is connected to a transmission line which carries an electrical signal that is transformed into electromagnetic radiation (in a transmitting antenna) or transformed from electromagnetic radiation (in a receiving antenna). An antenna design ideally meets desired criteria for gain, polarization, performance, bandwidth requirements, and other criteria while maintaining size, profile, and weight at a minimum. Furthermore, the antenna should be simple, inexpensive, and easy to manufacture.
Parabolic reflector antennas are highly directional (high gain) antennas that include a parabolic reflector to provide directional characteristics. For this reason, many point-to-point communication systems currently use parabolic reflector antennas. However, even though parabolic antennas typically provide for good wide band communication, they are much larger and thicker than flat panel or planar antenna structures. The bulky and unstable structure of parabolic antennas is also susceptible to high winds and other deleterious effects that may cause the antenna to fall or collapse. While stabilizing support may be provided for the antenna structure, this leads to additional costs and space requirements.
As a result, the use of much more compact planar or flat panel integrated antenna arrays has steadily increased over the past few years in the microwave frequency band, and the popularity of such flat panel antennas is similarly expected to rise in millimeter wave communication. Slot antenna elements fed by a printed transmission line such as a microstrip line, can provide a low overall profile or thickness (as described, for example, in applicant""s U.S. patent application No. 09/316,942, now U.S. Pat. No. 6,317,094, issued on Nov. 13, 2001). However, printed antenna feed structures exhibit a relatively low gain.
A slotted waveguide linear array can be formed by placing a number of suitably oriented slot antenna elements periodically along a waveguide transmission line. The antenna elements may take different forms, such as tapered slot antenna elements. The slots radiate power from the incident waveguide mode that may then be reflected by a terminal short circuit to create a narrow-band resonant array. Alternatively, if the residue of the incident wave is absorbed by an impedance matched load, then the array generates a broadband travelling wave. Waveguide fed slot arrays provide much better antenna efficiency and gain than printed antenna arrays, because waveguides exhibit much lower transmission loss than printed transmission lines. However, a drawback associated with prior art waveguide feed networks, for example that disclosed in U.S. Pat. No. 4,952,894, is that the overall array size is typically larger, particularly in terms of the thickness or profile of the array. In addition, because waveguide networks typically have a larger size or profile than printed transmission lines, it may be difficult to use a waveguide network in an array in which the antenna elements are tightly spaced. Furthermore, many antenna designs are required to exhibit a wide band characteristic. While a waveguide network can be designed to provide wide-band operation, a waveguide network with carefully designed bends and junctions is required to avoid undesirable band-limiting effects. These design restraints may result in additional manufacturing expense and complexities.
For example, U.S. Pat. No. 5,243,357 to Koike et al. discloses a square waveguide network for a receiving antenna array capable of separating both horizontal and vertical polarization components. To reduce the bulky profile of the waveguide network, the inventors describe a non-corporate feed waveguide network which can be made relatively flat and of low profile by providing a difference of one half the inter-waveguide wavelength between the length of the waveguide section connecting an antenna element to a first input branch of a waveguide junction and the length of the waveguide section connecting an adjacent antenna element to a second input branch of the waveguide junction. As a result, the waves at the first and second input branches of the waveguide junction have opposite polarizations (i.e opposite phase), and the resulting wave in a third output branch of the junction is the sum of the two (instead of the difference). In this manner, the waveguide network can be arranged so that it has bends in only a single plane, avoiding the large profiles associated with most prior art waveguide networks when the number of antenna elements increase. However, although it exhibits a low profile, proper operation of this embodiment of the waveguide network of Koike et al. is heavily dependent on the length of waveguide sections relative to the inter-waveguide wavelength in order to provide accurate summing of waveguide components. Consequently, the instantaneous bandwidth of the network is very small, and it is not suitable for wide band applications in which the wavelength inside the waveguide varies significantly. Furthermore, because this waveguide network effectively bends only in a single plane, and because it requires a difference of one half the inter-waveguide wavelength between two adjacent antenna elements, the network of Koike et al. may not be capable of feeding tightly spaced antenna elements and also consumes a greater footprint (i.e. the length and width of the network) than a waveguide network that bends in two planes.
Thus, there is a need for a waveguide network for feeding an array of slot antenna elements that is compact, has a low profile, exhibits a good wide band characteristic, and is optimized for high volume and low cost manufacturing.
It is an object of the invention to provide an improved waveguide network.
In a first aspect, the present invention provides a waveguide network having a first port; a plurality of second ports oriented in a first direction; and a plurality of waveguide junctions and waveguide bends. Each junction has a common branch and two separate branches. Each bend has a first branch and a second branch meeting at an angle, the junctions and bends being grouped into a plurality of sets with a particular set being denoted by n, n being an integer ranging from 0 to (N-1) and N representing the total number of sets and being an integer greater than or equal to three. The 0""th set is a first set, and the n""th set has 2n junctions and 2n+1 corresponding bends. Each of the separate branches of each junction in a particular set is connected to a first branch of a bend in the same set. The plurality of sets comprise E-plane sets operatively coupled with H-plane sets in an alternating fashion, each E-plane set comprising E-plane junctions and E-plane bends, and each H-plane set comprising H-plane junctions and H-plane bends. The common branch of the junction in the first set is connected to the first port. The second branch of each of the bends in the n""th set, other than the last set, is connected to the common branch of a junction in the (n+1)""th set, and the second branch of each of the bends in the last set is connected to one of the plurality of second ports. In addition, the second branches of each of the bends in at least one set lead extend in the first direction, and the second branches of each of the bends in at least one other set, not including the last set, extend in a direction opposite to the first direction.
Preferably, the first and second branches of each waveguide bend meet at an angle substantially equal to 90xc2x0, the separate branches of the waveguide junctions are generally collinear to one another, and the common branches of each waveguide junction intersects the two separate branches of that junction generally orthogonally. Also preferably, the second branches of each bend in each set, other than the first set, extend in a direction opposite to the second branches of each bend in the previous set. Each second port may be generally connected to a respective antenna element.
The waveguide network may comprise a plurality of separate pieces including a first piece containing all of the E-plane junctions and E-plane bends and a second piece containing all of the H-plane junctions and H-plane bends, the first and second pieces abutting one another when the waveguide network is assembled.
In another aspect, the present invention provides a waveguide network for connecting a first port to a plurality of second ports, the second ports being oriented in a first direction. The waveguide network comprises at least three successive sets of junctions and bends including a first set connected to the first port, a last set connected to the plurality of second ports and at least another set operatively coupled to a preceding set and a following set. The junctions and bends in each set are one of (i) E-plane junctions and E-plane bends and (ii) H-plane junctions and H-plane bends. Successive sets alternate between a set of E-plane junctions and E-plane bends and a set of H-plane junctions and H-plane bends. Advantageously, the waveguide bends in at least one set extend in the first direction, and the waveguide bends in at least one other set, not including the last set, extend in a direction opposite to the first direction. Preferably, each bend in each set, other than the first set and the last set, leads in a direction opposite to the direction in which the bends in the previous set lead.
The objects and advantages of the present invention will be better understood and more readily apparent with reference to the remainder of the description in conjunction with the accompanying drawings.